[Technical Field Pertinent to the Invention]
This invention relates to an image formation apparatus using electrophotography such as a copier and a printer and semiconductive members such as a semiconductive belt and a semiconductive roll used appropriate with the image formation apparatus and in particular to a charging roll for uniformly charging the surface of an image support in a copier, a printer, etc., a transfer roll for transferring a toner image formed on the image support to a record medium, a transfer toll for once transferring a toner image formed on the image support to an intermediate transfer body, a transfer roll for transferring the toner image once transferred to the intermediate transfer body to a record medium such as paper, a semiconductive roll used with a cleaning roll, etc., for removing the toner image on the image support, a semiconductive belt used as a paper transport body for transporting the intermediate transfer body and paper, and an image formation apparatus comprising at least one of the semiconductive members.
[Related arts]
An image formation apparatus using electrophotography forms uniform charges on an image support made of a photoconductive photosensitive body made of an inorganic or organic material and forms an electrostatic latent image with laser light, etc., modulated based on an image signal, then develops the electrostatic latent image in charged toner to form a visible toner image. The image formation apparatus electrostatically transfers the toner image via an intermediate transfer body or directly to a transfer body of paper, etc., thereby providing any desired reproduced image.
Particularly, as an image formation apparatus adopting the system of primarily transferring the toner image formed on the image support to the intermediate transfer body and further secondarily transferring the toner image on the intermediate transfer body to paper, an apparatus disclosed in JP-A-62-206567, etc., is known.
It is proposed to use a semiconductive endless belt comprising carbon black loaded to thermoplastic resin of polycarbonate resin (JP-A-3-89357, JP-A-06-095521), PVDF (polyvinylidene fluoride) (JP-A-5-200904, JP-A-6-228335), polyalkylene phthalate (JP-A-6-149081), PC (polycarbonate)/PAT (polyalkylene terephthalate) blend material (U.S. Pat. No. 2,845,059), ETFE (ethylene tetrafluoroethylene copolymer)/PC, ETFE/PAT, PC/PAT blend material (JP-A-6-149079), etc., as material of the intermediate transfer body used with the image formation apparatus adopting the intermediate transfer body system.
However, it is very difficult to control the resistance value of a resin material in a semiconductive region and it is almost impossible to stably provide any desired resistance value with normal conductive carbon black loaded to a normal resin material. Thus, the resistance values of all semiconductive endless belts need to be measured for selection and therefore costs are increased.
As described in xe2x80x9cKoubunshikakou, vol.43, Nov. 4, 1977, SUMITA et al.,xe2x80x9d as carbon black is loaded into a high polymer of resin material, etc., conductivity is small while a small amount of carbon black is loaded. From one threshold value, carbon black forms a conductor circuit and conductivity is enhanced rapidly and a medium resistance value cannot be provided.
Further, as a belt material used with the image formation apparatus adopting the intermediate transfer body system, JP-A-9-305038 and JP-A-10-240020 propose an elastic belt containing a reinforcing material comprising woven cloth of ester, etc., and elastic member laminated on each other.
However, the elastic belt involves a problem of occurrence of age extension caused by belt tension at the driving time.
JP-A-10-264268 discloses an attempt to decrease age extension of a belt at the driving time by heating resin or rubber reinforced with fibers in an expansion state for decreasing variations in inner peripheral length and providing a belt excellent in dimension stability.
However, this method has the disadvantage that it takes much time and labor as a manufacturing method, increasing the manufacturing costs.
Thus, although a large number of attempts have been made, variations in resistance values in members are large and it is difficult to stably provide members having uniform resistance values and decrease age extension at the belt driving time at low costs.
If in-plane variations in volume resistivity of intermediate transfer body (xcex94R) are large, particularly in a color image, a partial color loss is caused by a partial transfer efficiency difference and uniform high image quality cannot be provided; this is a problem.
The volume resistivity of an intermediate transfer body must be controlled in a predetermined range to provide high transfer image quality, in-plane variations in the intermediate transfer body (resistance value difference between the maximum and minimum values) must be small, and if the operating environmental condition changes, the volume resistivity must not largely change and high quality must be provided stably. For example, in practical use, it is required that volume resistivity change in a low-temperature and low-humidity environment of 10xc2x0 C. and 15%RH and a high-temperature and high-humidity environment of 28xc2x0 C. and 85%RH be within 1.5 orders of magnitude (logxcexa9 cm).
To give conductivity to material forming an intermediate transfer body, a method of giving a conductive agent giving electronic conductivity into composition material and a method of giving a conductive agent giving ion conductivity are available.
With a resin material comprising carbon black of a conductive agent giving electronic conductivity dispersed solely, the volume resistivity responsive to environmental change of temperature and humidity less varies, but it is difficult to uniformly disperse carbon black and thus in-plane variations in volume resistivity become easily large; this is a problem.
To give a conductive agent giving ion conductivity, volume resistivity change in the plane of the intermediate transfer body is extremely small, namely, 0.6 orders of magnitude (logxcexa9 cm) or less. In contrast, the volume resistivity responsive to environmental change of temperature and humidity varies largely. For example, the resistance value difference between the high-temperature and high-humidity environment of 28xc2x0 C. and 85%RH (H/H environment) and the low-temperature and low-humidity environment of 10xc2x0 C. and 15%RH (L/L environment) is 1.5 to tour orders of magnitude (logxcexa9 cm); this is a problem.
In an electrophotographic image formation apparatus, a semiconductive roll is often adopted. As the semiconductive roll, the following roll is often used: A conductive substance of carbon black, metal oxide, organic or inorganic electrolyte, etc., is dispersed in general elastomer (elastic body) such as EPDM (ethylene propylene diene rubber), NBR (nitrile butadiene rubber), SBR (styrene butadience rubber), polyurethane rubber, silicone rubber, or Norsorex to give conductivity, and the outer periphery of a conductive metal core is coated with a conductive foam elastic body foamed by machine foaming in air, nitrogen or with a chemical foaming agent to form a roll.
To control the electrical characteristic of a semiconductive roll, a method of changing the conductive agent blend amount in a conductive foam is known, but it is difficult to balance resistance because the hardness and resistance of the conductive foam is contrary to each other. With a semiconductive roll having electronic conductivity, control in a medium resistance region of 106 to 1012 xcexa9 cm is hard to perform, and resistance variations in semiconductive roll or between rolls are large; this is a problem.
It is very difficult to control the resistance value of a resin material in a semiconductive region; as with the above-mentioned semiconductive endless belt, it is almost impossible to provide any desired resistance value with normal conductive carbon black loaded to a normal resin material.
To resolve this problem, JP-A-10-254515 proposes a semiconductive roll comprising two types of carbon black different in characteristic dispersed in a foam elastic body having a sea island structure of three types of rubber materials different in solubility parameter value.
JP-A-11-22719 proposes a charging roll comprising a thermoplastic elastomer layer having volume specific resistance of 106 to 109 xcexa9 cm and a resin material layer of 1010 xcexa9 cm or less.
JP-A-11-45013 discloses that carbon black of a particular specific surface area is loaded to a rubber mixture of EPDM and NBR to provide an OA machine member whose resistance value is controlled.
However, also in a large number of these attempts, resistance value variations in roll member are large and it is difficult to stable provide members having a uniform resistance value.
A semiconductive roll of ion conductivity type wherein an antistatic additive of fourth-grade ammonium salt, etc., and inorganic and organic electrolytes of alkaline metal, etc., are loaded has extremely small in-roll resistance variations and is desirable, but involves a problem of large resistance value change responsive to environmental change of temperature, humidity, etc.
If in-plane volume resistivity variations of semiconductive roll (xcex94R) are large, for example, to use the semiconductive roll as a charging roll, an image support is charged unevenly and in a transfer roll, particularly in a color image, a partial color loss, etc., is caused by a partial transfer efficiency difference and uniform high image quality cannot be provided; this is a problem.
Further, in the related art, to use semiconductive rolls of conductive foam elastic bodies as a charging roll and a transfer roll, the volume resistivity partially changes because of deposition of toner, etc.; this is a problem.
JP-A-6-149097 proposes a roller (bias roller) characterized in that the roller surface of a silicon foam rubber body is coated partially with a fluorine resin or a silicone resin like fine spots. JP-A-6-175470 proposes a conductive roller provided by forming the roller surface of a urethane foam rubber body of a soluble fluorine resin with a conductive material blended.
However, asperities of foam cells occur on the surface of every foam rubber member. Thus, if the surface layer is coated with a fluorine-family resin, the scrape effect of a cleaning blade cannot sufficiently be exerted and there is a problem of occurrence of toner dirt.
[Problem to be Solved by the Invention]
It is therefore an object of the invention to provide semiconductive members such as a semiconductive belt and a semiconductive roll improved in uniformity of electric resistance with less change in electric resistance depending on the environment, and an image formation apparatus using such semiconductive members to provide high-quality images stably.
[Means for Solving the Problem]
To the end, according to the invention, there is provided a semiconductive member having a portion formed of a thermoplastic elastomer composition comprising a thermoplastic resin as a matrix and rubber particles at least some of which have conductivity and at least some of which are cross-linked as domain.
In the semiconductive member of the invention, preferably the ratio between viscosity of the thermoplastic resin, xcex7m, and viscosity of a rubber component forming the rubber particles when the rubber component is not cross-linked or is being cross-linked, xcex7r, is
0.5 less than xcex7r/xcex7m less than 1.5 
Preferably, the thermoplastic resin is made of at least one resin selected from the group consisting of polyamide family resin, polyester family resin, polyimide family resin, polysulfide family resin, polysulfone family resin, styrene family resin, olefin family resin, and urethane family resin. Preferably, the rubber particles contain ketjen black and carbon black with an oil absorption amount of 0.5 cc/g or more.
The first semiconductive belt of semiconductive belts of the invention provided to the end is a semiconductive belt having a base material and a surface layer, wherein the base material is formed of a thermoplastic elastomer composition comprising an insulating thermoplastic resin as a matrix and rubber particles at least some of which have conductivity and at least some of which are cross-linked as domain, the semiconductive belt having a Young""s modulus of 500 MPa or more and volume resistivity of 107 to 1013 xcexa9 cm.
The second semiconductive belt of semiconductive belts of the invention has a thermoplastic elastomer member formed of a thermoplastic elastomer composition having a thermoplastic resin as a matrix and rubber particles at least some of which are cross-linked as domain and comprising the rubber particles at least some of which have conductivity with the volume specific resistance value of the rubber particle being smaller than that of the thermoplastic resin, Young""s modulus being 500 MPa or more, the volume specific resistance value being 106 to 1013 xcexa9 cm, and variations in volume specific resistance value (R) being within to the power of one.
In the first and second semiconductive belts of the invention, preferably the thermoplastic resin has a Young""s modulus of 1000 MPa or more, the rubber particle has volume resistivity of 107 xcexa9 cm or less, and the thermoplastic elastomer composition has a volume fraction of thermoplastic resin/rubber particles =30/70 to 90/10 between the thermoplastic resin and the rubber particles.
In the first and second semiconductive belts of the invention, preferably the ratio between viscosity of the thermoplastic resin, xcex7m, and viscosity of a rubber component forming the rubber particles when the rubber component is not cross-linked or is being cross-linked, xcex8r, is
0.5 less than xcex7r/xcex7m less than 1.5 
The thermoplastic resin may be made of at least one resin selected from the group consisting of polyamide family resin, polyester family resin, polyimide family resin, polysulfide family resin, and polysulfone family resin. Preferably, the rubber particles contain ketjen black and carbon black with an oil absorption amount of 0.5 cc/g or more.
Further, in the first semiconductive belt of the semiconductive belts of the invention, preferably the surface layer is a low surface energy layer made of a material having lower surface energy than the base material, in which case preferably the surface layer is made of a material consisting essentially of fluorine family resin or a material comprising fluorine family resin powder dispersed.
Further, preferably the first and second semiconductive belts of the invention are molded by cylindrical molding.
The first semiconductive roll of semiconductive rolls of the invention provided to the end comprises a core, a foam surrounding the core, and an elastic layer formed of a thermoplastic elastomer composition comprising an insulating thermoplastic resin as a matrix and rubber particles at least some of which have conductivity and at least some of which are cross-linked as domain, surrounding the foam, and has ASKER C hardness of 25 to 70 degrees and volume resistivity of 104 to 1012 xcexa9 cm.
The second semiconductive roll of semiconductive rolls of the invention is a roll comprising a thermoplastic elastomer member formed like a cylinder on the outer periphery of a core with the thermoplastic elastomer member being formed of a thermoplastic elastomer composition having a thermoplastic resin as a matrix and rubber particles at least some of which are cross-linked as domains and comprising the rubber particles at least some of which have conductivity with the volume specific resistance value of the rubber particle being smaller than that of the thermoplastic resin, JIS A hardness being 25 to 50 degrees, the volume specific resistance value being 106 to 1012 xcexa9 cm, and variations in volume specific resistance value (R) being within to the power of one.
In the first semiconductive roll of the semiconductive rolls of the invention, preferably the thermoplastic resin has a tensile elastic modulus of 50 MPa or less, the rubber particle has volume resistivity of 108 xcexa9 cm or less, and the thermoplastic elastomer composition has a volume fraction of thermoplastic resin/rubber particles =25/75 to 90/10 between the thermoplastic resin and the rubber particles.
In the second semiconductive roll of the semiconductive rolls of the invention, preferably the 100% tensile elastic modulus of the matrix is 50 MPa or less, the volume specific resistance value of the domain is 106 xcexa9 cm or less, and the volume fraction of the domain to the matrix is 10/90 to 90/10.
In the first and second semiconductive rolls of the invention, preferably the ratio between viscosity of the thermoplastic resin, xcex7m, and viscosity of a rubber component forming the rubber particles when the rubber component is not cross-linked or is being cross-linked, xcex7r, is
0.5 less than xcex7r/xcex7m less than 1.5 
The thermoplastic resin may be made of at least one resin selected from the group consisting of styrene family resin, olefin family resin, urethane family resin, polyamide family resin, and polyester family resin.
Preferably, the rubber particles contain black and carbon black with an oil absorption amount of 0.5 cc/g or more.
Further, preferably the first semiconductive roll of the semiconductive rolls of the invention comprises a low surface energy layer made of a material having lower surface energy than the elastic layer on the elastic layer, in which case preferably the low surface energy layer is made of a material consisting essentially of fluorine family resin or a material comprising fluorine family resin powder dispersed.
The first image formation apparatus of image formation apparatus of the invention provided to the end is an image formation apparatus for charging a predetermined photosensitive body, applying exposure light responsive to an image to the photosensitive body, thereby forming an electrostatic latent image on the photosensitive body, developing the electrostatic latent image in toner, thereby forming a toner image on the photosensitive body, and finally transferring the toner image onto a predetermined record medium and fixing the toner image, thereby forming an image made of the fixed toner image on the record medium, characterized in that
the image formation apparatus comprises a semiconductive belt having a base material being formed of a thermoplastic elastomer composition comprising an insulating thermoplastic resin as a matrix and rubber particles at least some of which have conductivity and at least some of which are cross-linked as domains and a surface layer formed on a surface of the base material, the semiconductive belt having a Young""s modulus of 500 MPa or more and volume resistivity of 107 to 1013 xcexa9 cm.
In the first image formation apparatus of the invention, the semiconductive belt may be an intermediate transfer belt for receiving transfer of the toner image from the photosensitive body and transporting the transferred toner image for transfer to the record medium or may be a paper transport belt for supporting the record medium and transporting the record medium via a position in contact with or in the proximity of the photosensitive body to receive transfer of the toner image from the photosensitive body on the record medium.
The second image formation apparatus of image formation apparatus of the invention is an image formation apparatus comprising an image support for forming an electrostatic latent image responsive to image information, a developing unit for visualizing the electrostatic latent image formed on the image support as a toner image in toner, an intermediate transfer body onto which the toner image supported on the image support is transferred, and a transfer unit for transferring the toner image transferred onto the intermediate transfer body to a record medium, characterized in that a material forming the intermediate transfer body has a thermoplastic elastomer member formed of a thermoplastic elastomer composition having a thermoplastic resin as a matrix and rubber particles at least some of which are cross-linked as domain and comprising the rubber particles at least some of which have conductivity with the volume specific resistance value of the rubber particle being smaller than that of the thermoplastic resin, Young""s modulus being 500 MPa or more, the volume specific resistance value being 106 to 1013 xcexa9 cm, and variations in volume specific resistance value (R) being within to the power of one.
The third image formation apparatus of image formation apparatus of the invention is an image formation apparatus comprising an image support for forming an electrostatic latent image responsive to image information, a developing unit for visualizing the electrostatic latent image formed on the image support as a toner image in toner, a transfer material transport unit having a conductive belt for transporting a transfer material to the image support to transfer the toner image supported on the image support to the transfer material, and a transfer unit for transferring the toner image on the image support to the transfer material, characterized in that the conductive belt has a thermoplastic elastomer member formed of a thermoplastic elastomer composition having a thermoplastic resin as a matrix and rubber particles at least some of which are cross-linked as domain and comprising the rubber particles at least some of which have conductivity with the volume specific resistance value of the rubber particle being smaller than that of the thermoplastic resin, Young""s modulus being 500 MPa or more, the volume specific resistance value being 106 to 1013 xcexa9 cm, and variations in volume specific resistance value (R) being within to the power of one.
The fourth image formation apparatus of image formation apparatus of the invention provided to the end is an image formation apparatus for charging a predetermined photosensitive body, applying exposure light responsive to an image to the photosensitive body, thereby forming an electrostatic latent image on the photosensitive body, developing the electrostatic latent image in toner, thereby forming a toner image on the photosensitive body, and finally transferring the toner image onto a predetermined record medium and fixing the toner image, thereby forming an image made of the fixed toner image on the record medium, characterized in that
the image formation apparatus comprises a semiconductive roll comprising a core, a foam surrounding the core, and an elastic layer formed of a thermoplastic elastomer composition comprising an insulating thermoplastic resin as a matrix and rubber particles at least some of which have conductivity and at least some of which are cross-linked as domain, surrounding the foam, and having ASKER C hardness of 25 to 70 degrees and volume resistivity of 104 to 1012 xcexa9 cm.
Further, the fifth image formation apparatus of image formation apparatus of the invention is an image formation apparatus for charging a predetermined photosensitive body, applying exposure light responsive to an image to the photosensitive body, thereby forming an electrostatic latent image on the photosensitive body, developing the electrostatic latent image in toner, thereby forming a toner image on the photosensitive body, and finally transferring the toner image onto a predetermined record medium and fixing the toner image, thereby forming an image made of the fixed toner image on the record medium, characterized in that a semiconductive roll comprising a thermoplastic elastomer member formed like a cylinder on the outer periphery of a core with the thermoplastic elastomer member being formed of a thermoplastic elastomer composition having a thermoplastic resin as a matrix and rubber particles at least some of which are cross-linked as domains and comprising the rubber particles at least some of which have conductivity with the volume specific resistance value of the rubber particle being smaller than that of the thermoplastic resin, JIS A hardness being 25 to 50 degrees, the volume specific resistance value being 104 to 1012 xcexa9 cm, and variations in volume specific resistance value (R) being within to the power of one is used.
In the fourth and fifth image formation apparatus of the invention, the semiconductive roll may be a charging roll for charging the photosensitive body or may be a transfer roll for transferring from a toner image support supporting the toner image before transfer to a toner image support for supporting the toner image after transfer.